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Windows Active Directory Site Costs

I was wondering if anyone had any recommendations on the site cost calculation.

For example: I have 3 Root Controllers,

1 = Europe
2= America
3= Canada

This is a multi-domain archeteructure so we whave over 50 child domains and 100 DCs.
The Canada domains seem to have the nearest replication topology to some of hte DC's in Europe which is causing some issues right now.

Question: In Site Cost between three Root Controllers, they are all setup to each other in sites and servcies at cost of 10 with replication of 45 minutes.

I have all the rest of the sites setup accordingly like sites in U.S. are setup to one link to the root controller in America.

So the question here is how do i make sure that all the sites in U.S. point to U.S. and etc. But seeing how my root controllers are setup, should I be changing the costs so that the U.S. sites don't get nearest path to a Europe domain controller? Any suggestions would be helpful.
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1 Solution
Mike KlineCommented:
So US, Europe, and Canada are all separate domains in the same AD forest.   What you can do is setup site links between the sites you want.

SO suppose in US you have

Main US HQ site
Remote Site 1
Remote Site 2

You could create a site link between USHQ and Site 1.  USHQ and Site 2 etc...this also all depends on your physical infrastructure.


shorisAuthor Commented:
Yes they are all separate .. root controllers.  They way i have it today is one site link setup with all three combined with the cost of 10 and replicate 45 minutes. Clearly, I can see the Europe picks up Canada DC's cause it finds the nearest path and that i don't want.

Have created all US Servers to site link with the US Root controller. But the question i had was that all three root controllers have a site link to each other and i was wondering if i should increase that cost??

The rest of the domains are setup correctly to their respective Regional link. But even though that is setup, a controller in Europe picks up automatic connection setting to a DC in Canada, and I dont want that.
Leon FesterSenior Solutions ArchitectCommented:
The root cause of your problem is the fact that you have all 3 root domain controllers in the same site. I'm assuming they each have their own subnets for their sites?

If yes, then you need to setup the site links to only include the sites that you want to as part of your replication topology.

So while all 3 sites containig your root DCs and are in the same site links you can see this issues arising. Create a site link with US and Europe only and another with US and Canada only. This way Canada and Europe will create automatic links.

Have a read about hub-and-spoke topology vs mesh topology, with that many domains and different geographical sites, you'll probably need a hybrid configuration.
shorisAuthor Commented:
I really appreciate your input. Makes complete sense.

Would do you think of this design then:

Root COntrollers:

US - Canada  Cost 250 and Replicate 45
US  -Europe Cost 300  andReplicate 60
CA-Euruope Cost 300 and replicate 60 minutes

multi-site - multi-site Cost 90 and 30 if needed.

What do you think?
Leon FesterSenior Solutions ArchitectCommented:
Adjusting the costs like that should give you the desired replication topology.
But the actual value cannot be accurately determined without knowing your network capacity.
Here is a handy guide for calculating your costs.

After implementing new costs, I usually ask the Network team to monitor the line consumption to see if I'm not causing a bottleneck with my AD replication.

The replication times are also dependant on a few factors:
e.g. most root domains I've come across have been resource only domains with little or no user accounts. In this scenario, you wouldn't have many issues with user account resets or permissions changes. Ideally this domain only hosts enterprise level resources like Exchange, Lync, etc. Most changes to these domains are planned activities and project work. By default the value for intersite replication is 180 minutes.

Determining when intersite replication occursActive Directory preserves bandwidth between sites by minimizing the frequency of replication and by allowing you to schedule the availability of site links for replication. By default, intersite replication across each site link occurs every 180 minutes (3 hours). You can adjust this frequency to match your specific needs. Be aware that increasing this frequency increases the amount of bandwidth used by replication. In addition, you can schedule the availability of site links for use by replication. By default, a site link is available to carry replication traffic 24 hours a day, 7 days a week. You can limit this schedule to specific days of the week and times of day. You can, for example, schedule intersite replication so that it only occurs after normal business hours. For more information, see Configure site link replication frequency and Configure site link replication availability.


With certain restrictions, you can use the Simple Mail Transfer Protocol (SMTP) for replicating to sites that do not have a direct or reliable Internet Protocol (IP) connection. For more information, see "Active Directory Replication" at the Microsoft Windows Resource Kits Web site.

Intersite replication through a firewall or virtual private network requires some special considerations. For more information, see Active Directory at the Microsoft Web site.

One last point re: costs...Exchange 2007 and higher is reliant on AD site costs to calculate delivery routes to servers so keep this in mind if you're running Exchange 2007 or higher.
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